The present disclosure relates to a mask for extreme ultraviolet lithography, and in particular, to a phase-shift mask for extreme ultraviolet lithography.
A reduction in size and design rule of a semiconductor device leads to an increasing demand for a technique to reduce a size of a pattern. In order to meet such a demand, a light source configured to emit light of a shorter wavelength in a lithography process may be used. For example, lights of 436 nm (“g-line”), 365 nm (“I-line”), 248 nm (e.g., of KrF laser), and 193 nm (e.g., ArF laser) have been used as light sources in the lithography process. Recently, the extreme ultraviolet (EUV) light of 13.5 nm has been suggested as a light source for EUV lithography.
Because most of the EUV light is absorbed by refractive optical materials, a reflective optical system, instead of a refractive optical system, is used in the EUV lithography.